Previously, a self-generated electrical power facility using a natural energy, such as a photovoltaic power system, a wind power system or the like has been configured such that a generated surplus power is reversely supplied (sold) to an electric power system, or is accumulated in a storage battery to be discharged from the storage battery when the demand for power becomes greater than the amount of power generated (for example, see Japanese Patent Application Publication No. 2006-311676).
However, when a surplus power from a self-generated electrical power facility, such as a photovoltaic power system or the like, exceeds even the demand for power selling and the charge capacity of the storage battery, the relevant surplus power has to be inevitably discarded and then wasted.